The present invention relates to an improved mixing process and apparatus of the type employed for the mixing of at least two fluid components of the type which when mixed together undergo chemical reaction to form a solid or semi-solid reaction product.
The use of multicomponent fluid reactive systems, generally liquid reactive systems, is well known and includes materials such as curable epoxy resins, curable polyurethane resins, curable polyester resins, curable silicone resins, curable polysulfide resins, curable phenolic resins and curable urea resins. These resins and their curing agents are known in the art. In the use of such materials, two or more fluid components, i.e. the resin and curing agent, for example liquid components, are mixed together in the required proportions, whereby the components undergo a chemical reaction resulting in a change of state, normally to a solid or semi-solid reaction product.
In most systems employing such materials, the reactive liquid starting components are internally mixed in mixing heads. Specifically, the reactive components are separately introduced into a mixer, the components are mixed within the mixer, at which time the chemical reaction begins, and the reaction mixture is discharged from the mixer prior to the completion of the chemical reaction and while still in a fluid state. After discharge from the mixer, the reaction mixture may be immediately employed in a production operation, for example a molding or injection operation to form a desired product.
The mixers employed in this type of operation are normally various known dynamic mechanical rotary mixers or mixers of the interfacial surface generator type. In the use of such mixers, the mixing operation is basically continuous. That is, for a given mixing operation, separate components are continuously introduced into the mixer and the reaction mixture is continuously discharged from the mixer.
It will be understood that whatever type mixer is employed, it is important that the reaction mixture be discharged from the mixer prior to the completion of the chemical reaction, i.e. before the "pot life" of the particular components is exceeded. If the chemical reaction is completed before the reaction mixture is discharged from the mixer, then the solid or semi-solid reaction product will jam the mixer.
Accordingly, when it becomes necessary to terminate a given mixing operation, for example at the end of a production run or at the end of a given production period, for example a work day or work week, it is current industrial practice to remove any remaining reaction mixture from the interior of the mixer. This is normally done by a manual or automatic flushing of the reaction mixture remaining in the mixer. This flushing normally necessitates the use of various solvents.
This present practice however has several distinct disadvantages. Specifically, if the flushing is carried out manually, then this requires a relatively skilled operator, inasmuch as the time allowed for achieving a flushing operation is relatively short. In the event that the operator makes an error and the chemical reaction is allowed to continue to completion within the interior of the mixer, then the mixer might well be permanently damaged. Even if the mixing system includes an automatic warning device to warn the operator upon shutdown of operation of the mixer, or even if the mixer includes an automatic flushing system, the flushing operation still represents a substantial operating cost. Specifically, flushing of the residual reaction mixture involves a wastage of the residual reaction mixture itself, in addition to a wastage of the solvents employed for the flushing operation. An additional disadvantage of this known system involves the increasing difficulty in providing a satisfactory manner of disposal of the resultant mixture of flushing solvent and residual reaction mixture. A further disadvantage of this known system is that storage of solvents presents a safety hazard, since many such solvents are flammable.
Thus, it will be apparent that known systems may not practically be employed for an intermittent flow movement of the components.